Work with methionine, choline, betaine and sarcosine comparing the oxidation of their methyl groups and dilution of methionine with these compounds showed that synthesis of phospholipid choline could not account for the oxidation of the methionine methyl group in short term experiments. The intermediate formation of sarcosine via the glycine methyltransferase enzyme could account for less than 20% of the oxidative catabolism of the methionine methyl group. S-methyl-cysteine depressed growth in the rat and causes similar tissue lesions to that observed with methionine. S-methyl-cysteine competes with methionine metabolism in the rat and in a liver homogenate system whereas S-adenosylmethionine does not, suggesting that a significant fraction of the oxidative catabolism of the methionine methyl group is independent of S-adenosylmethionine formation. Cystine at high concentrations in low methionine diets depresses methionine oxidation apparently by enhancing protein synthesis. BIBLIOGRAPHIC REFERENCE: Case, G.L., A.D. Mitchell, A.E. Harper and N.J. Benevenga. 1976. Significance of choline synthesis in the oxidation of the methionine methyl group. J. Nutr. (in press).